Electrical circuits



Patented Mar. 24, 1925.

UNITED STATES 1 1,530,613 PATENT caries.-

PA UL PIERCE, 01? NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY,

INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OI'JNEW YORK.

ELECTRICAL cmcurrs.

Application flled september 16, 1920. Serial 110. 410,587.

To all whom it may concern.

Be it known that I, PAUL H. PIERGEB. citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Electrical Circuits, of which the following is a full, clear, concise, and exact description.

This invention relates to electrical circuits and more particularly to circuits and apparatus adapted to be associated with repeaters and amplifiers of alternating currents.

An object of the invention is to provide a transformer which will have a uniform transmission efliciency over a wide range'of frequencies.

- reactance.

In vacuum tube repeaters used for telephone transmission, the secondary of an input transformer is usually connected directly to the input electrodes of the vacuum tube. The input electrodes, the leads from the transformer, and the coils of the transformer itself have, a small capacity. At the lower frequencies of the voice range, however, the capacity reactance is so small that the secondary is practically open circuited and the transformer presents to the line an inductive reactance. At the upper frequencies of the voice range the capacity reactance becomes considerable, and the transformer presents to the line a capacity It has been found that the in' ductive reactance can be annulled at the lower frequencies by a condenser connected in series with one of the transformer coils, preferably the primary, and that the capac ity reactance can be annulled by the insertion of a suitable inductive reactance.

The invention further resides in the spe-' ing drawings, in which Fig. 1 represents P schematically a circuit embodying the iii-- vention, and Fig. 2 represents a modified method of inserting reactance.

Referring to the drawings by reference numerals, .conductors 5 and 6 which may, for example, be telephone line wires, are connected to the outer terminals of a potentiometer 8 which is adjustably connected to theprimary 10 of transformer 11. The secondary 12 of transformer 11 is connected to the cathode l5 and gridv or control electrode 16 of the vacuum tube amplifier 17. A source of potential 18 is employed to maintain the grid negative with respect to. the cathode. Cathode and anode 19 may be connected by meansof any usual or desired output circuit to the conductors and 26, which may, for example, be the outgoing line wires.

Since the vacuum tube amplifier is a voltage operated device, transformer 11 is arrange to step up the voltage. It may, for example, have an. impedance step up ratio of 282 to 300,000 ohms. The input impedance of vacuum tube 17 with reference to direct current or low frequencies is usually of the order of infinity and in any eventis high relative to the impedance of the high impedance winding of the transformer. At the higher frequencies of the voice range, however, the capacity between the tube electrodes, the capacity between the'leads, and the capacity within the coil itself are appreciable. 'For these reasons the transformer presents an inductive reactance to the line in the lower part "of the voice range and a capacity reactance in the upper part of the voice range. If these reactances are not annulledthe repeater may give a desired gain in the middle portion of the frequency range, but the transmission may fall off considerably .at the upper and lower ends of the range, with resulting distortion of the speech signals. This would also result in poor transmission of ringing currents, which in practice usually have a low frequency, as for example, 135 cycles.

An inductance is provided in series with primary 10'having such a value that V it will. resonate with the'capacity reactance above described at frequencies up to the upper end of the range of frequencies which it is desired to transmit. As disclosed in the application of W. L. Casper, Serial No. 366,581, filed March 17, 1920, the inductive reactance employed to annul the capacity reactance may have the form of a separate inductance as shown in Fig. 1,or it may be obtained by introducing leakage in the transformer itself, as'indicated in dotted lines at 30 in Fig. 2, since the leakage inductance in a transformer is equivalent to an inductance in series with the primary winding. I

A condenser 32 is provided to annul the inductive reactance of the transformer at frequencies in the lower part of thevoice range. This condenser 1s preferabl of such a value that it will resonate wit the inductive reactance at the frequency of the ringing current employed,.wh1ch, as above stated, ma be 135 cycles. The selfinductance-oft e rimary winding 10 is made large so that the condenser 32 ma be small enough to substantially prevent t e flow of telegraph signals, which may, for exam le, have a frequency of the order of cyc es.

The potentiometer 8 is made up of a plurality of resistances 34 connccte in series and having taps therebetween thatmay be selectively connected by means of a contact or contacts 36 to the primary 10.- It has been found with the types of potentiometer-s heretofore employed that when the contacts "corresponding to contacts 36 were adjusted to vary the repeater gain, thus varying the proportion of the resistance connected 1n series with the primary 10, this so changed the constants of the circuit comprising primary 10 and associated elements that the transmission characteristics was no longer ,uniform, even though the circuit had been scribed and claimed in the application of D. F. Whiting, Serial No. 406,861, filed Aug.

. While the invention has been shown in connection with a vacuum tube repeater, it is obvious that certain features of the invention are capable of a variety of uses and that the invention is not to be limited except as defined in the following claims.

What is claimed is:

1. In combination with a transformer presenting in its primary circuit an inductive reactance at low frequencies, and a capacity reactance at relatively high frequencies, means for resonating with said reactances respectively.

2. In combination with a trans former presenting in its primary circuit an inductive reactance at low frequencies, and a capacity reactance at relatively high frequencies, a condenser for tuning with said inductive reactance at one of said low frequencies and an inductive reactance for annulling said capacity reactance at one of said relatively high frequencies.

3. In combination with a transformer presenting in its primary circuit an inductive 4. In combination with a transformer having its secondary terminals connected through a small capacity only, whereby said transformer presents in its primary circuit a capacity. reactance at certain frequencies and an inductive reactance at lower frequencies, an inductance forming with said capacity reactance a tuned circuit at one frequency, and a condenser forming with said inductive reactance a tuned circuit at a lower frequency.

5. In combination with a transformer having its secondary terminals connected through a small capacity only, whereby said transformer presents in its primary circuit a capacity reactance at frequencies in the upper part of the voice range and an induetive reactance at frequencies in the lower part of the voice range, an inductance formin with said capacity reactance a tuned circult at one frequency and a condenser forming with said inductive reactance a tuned circuit at a lower frequency.

6. In combination, a transformer having its secondary terminals connected through an impedance high relative to the impedance looking into the transformer from said terminals, means for raising the transmissionfrequency characteristic of said transformer over one frequency range, said means comprising a condenser effectively in series with a winding of said transformer, and'means for improving the transmission-frequency characteristic of said transformer over a different frequency range, saidlast mentioned means comprising an inductive reactance effectively in series with said winding.

7. In combination, a transformer having its secondary terminals connected through a relatively high impedance, a condenser and an inductlve reactance effectively in series ing a transformer, said amplifier and said transformer having a tendency to transmit intermediate frequencies of said band more efficiently than the upper and the lower frequencies thereof, and said input circuit comprising tuned circuits for increasing the transmission efficiency at said upper frequencies and at said lower frequencles.

9. A circuit comprising an electron discharge device, an input transformer therefor, and a source for sup lying a band of frequencies to said trans ormer, said circuit including capacity effectively in shunt to the secondary of said transformer, said transformer and amplifier comprising inductances such that the impedance looklng into the rimary of the transformer is inductive at t e lower frequencies of said band and capacitative at the upper frequencies of said band, one of said inductances being effectively in series with said source and forming with said capacitative impedance a circuit resonant at a frequency 1n the ne1gh-- borhood of the upper limit of said band,

and said first mentioned circuit comprising "a capacity effectively in series with another of said inductances and resonatin therewith at a frequency in the lower portion of said band.

10. A circuit comprising an electron discharge amplifier, an input transformer therefor, and a source for supplying a curtance effectively in series with sald source" and with at least a portion of said capacity and forming a circuit resonant at a frequency higher than said intermediate frequency for counteracting the tendency of said shunt capacity to lower the transmission efliciency of said circuit at the. upper end of said band of frequencies, and said circuit comp-rising capacity effectively in series with said inductance of saidtransformer and resonating therewith in the lower portion of said frequency band.

11. In combination, a line, a vacuum tube amplifier coupled to said line for repeating a band of frequencies in said line, said amplifier having aii anode, a cathode and a c0l1- trol electrode, said amplifier having an appreciable ca-pacityefi'ect between its control electrode and cathode, said capacity effect making the amplifier less efficient to trans mit the upper frequencies than the intermediate frequencies of said band, a capacity in series with said line, and means connected between said line and said amplifier, said means producing an inductive eflc'ect acting effectively in series with said line for resonating with said first capacity at such a frequency as to substantially equalize the transmission of said upper frequencies, and said means comprising an inductance resonating with said second capacity at such a frequency as to substantially equalize transmission of the lower frequencies of the band.

12. In combination, an amplifier having input and output circuits arranged to repeat in substantially the same wave form a wide band of speech frequencies with substantially constant transmission for all frequencies in said band, an incoming line, said amplifier having input electrodes and a transformer coupling said electrodes to said line, said input electrodes having an appreciable capacity effect therebetween acting as a shunt across said line and tending to decrease the transmission efiiciency of said amplifier for said band an amount increasing with the frequency, means resonating with said capacity to substantially overcome the decrease in transmission efliciency'caused by said capacity effect over a wide range of frequencies in said band, said transformer havlng an inductance tending to decrease the transmission efficiency of said amplifier at frequencies in the lower portion of said band, and a capacity in serial relation to said line and resonating with said trans former inductance insaid lower portion of said band and substantially equalizing trans-, mission over a wide range of frequencies in said lower portion of said band.

13. In combination, a transformer presenting in its primary circuit an inductive reactance to frequencies in the lower part of a range of frequencies to be transmitted therethrough and a capaoitative reactance to frequencies in the upper part of said range, and means for annulling each of said reactances to a substantial degree.

14. In combination, a transformer presenting in its primary circuit an inductive reactance to frequencies in the lower part of a range of frequencies to be transmitted therethrough and a capacitative reactance to frequencies in the upper part of said range, a condenser for annulling said inductive reactance to a substantial degree and an in uctancefor annulling said capacitative 1'15 reactance to a substantial'degree, said condenser and said inductance being connected in series with the primary winding of said transformer. a

In witness whereof, I hereunto subscribe rlny name this 13th day of September, A. D.

PAUL H. PIERCE. 

